Electronic devices that are used to detect gases are sometimes referred to as “electronic noses” or “artificial noses.” Similar devices are available for detecting liquids. Possible uses include identifying a presence of an unhealthy environment and identifying constituents of a liquid or gas. Goals in the design of gas-detection and liquid-detection devices include minimizing costs and maximizing reliability and speed.
There are a number of different approaches to detecting and/or identifying fluids (i.e., analytes). One approach is to employ conductive transducers that change electrically when particular molecules are introduced. The electrical change may be with respect to resistance or capacitance. The transducers may be an array of metal oxide pads or chemically absorbent pads which have different specific reactions to analytes. With properly designed arrays, each of a number of different gases will have a unique characteristic set of resistance/capacitance values when the array of transducers is exposed to the gas.
A second general-category approach to designing an electronic nose is to include absorbent polymers in a quartz crystal microbalance (QCM) system. The absorbent polymers will have masses that vary as different molecules are absorbed. As a result, the resonant frequency of the system will change in dependence upon the molecules to which the polymers are exposed. A third approach is similar, since frequency changes are used to identify analytes. In this third approach, a surface acoustic wave (SAW) system is involved, with the frequency variations being with respect to travel along a surface, rather than through a bulk material.
There are at least two optical approaches. In one such approach, the electronic nose includes an array of transducers which are chemically active fluorescent dyes. As analytes interact with the fluorescent dyes, light is generated by the various dyes. The frequencies of the emitted lights are used to identify the gas or gas components. The other optical approach is to utilize dyes which merely change spectral characteristics (color) as a reaction to exposure to fluid molecules.
While the available approaches operate well for their intended purposes, one concern is that sensing results may be influenced by external factors, such as temperature.